Side-by-side specifications of the Synology RS815 and RS820+, from official datasheets. Differences are highlighted.
| RS815 | RS820+ | |
| CPU | dual-core CPU | Intel Atom C3538, 2.1 GHz |
| Cores / threads | 2 cores / 2 threads | 4 cores / 4 threads |
| RAM (base) | 1 GB DDR3 | 2 GB DDR4 non-ECC |
| RAM (max) | 1 GB | 18 GB |
| Drive bays | 4 | 4 |
| Expandable to | 4 | 8 total with RX418 |
| M.2 slots | 0 | 0 built-in; optional M2D18 via PCIe |
| Network | 2x Gigabit | 4× Gigabit Ethernet |
| 10GbE | no | optional |
| Max raw capacity | 32 TB | 56 TB raw (4×14 TB); 112 TB with RX418 |
| Hot-swap | yes | yes |
| Form factor | 1U rackmount | 1U rackmount |
| Released | 2015 | 2020 |
| Power consumption | — | unknown |
| DSM at launch | — | unknown |